Not only is it a matrix, but it appears that the matrix scan connections are
available at the expansion connector. It should be quite straightforward to
deterine whether there's a faulty/inermittent connection and to isolate it.
It's just a matter of the associated tedium. That was why I suggested that the
on-board keypad could be replaced with an off-board one connected in a similar
fashion to the applicaton connector. That will "buy time" to find a suitable
replacement, and it will provide a replacement to use in the meantime, also
allowing the owner to regain confidence in the remaining functions on the board.
Moreover, it allows for the possiblility that there's a problem with the board
itself, i.e. intermittent trace, etc. If the external keypad connected to the
expansion connector doesn't work consistently either, it suggests there's a
problem with the board itself. Likewise, if the problem presently on the board
doesn't go away when wires are soldered in parallel with the existing
matrix-scanner device connections, presumably a PIA or VIA, then it's likely
that the device itself may have been damaged, though I have a bit of trouble
imagining a circumstance that it would become intermittent if its solder
connections are sound.
What's most likely, however, is that the connections or traces have been damaged
over years of pressing on the keypad and thereby flexing the board. The simple
way to get around that is to solder on the fewer than two-dozen wires used to
hook up the keypad and expansion connector, and proceed from there.
Ideally, one would generate a test routine for the KIM that would echo via a
parallel port, say, the value associated with the scan of the keypad. This
would be monitored by an external PC. That same PC would drive a matrix of SPST
relays wired in the same matrix as the keypad and attached, in one instance to
the physical switch connections on the underside of the KIM-1's keypad, and in
another at the expansion connector.
After running it over a long time, e.g. a day or weekend, and logging, in the
PC, the time and date of each failure, one could then proceed to perturb the
circuit board, i.e. push on the keypad to see if it causes the externally
generated switch closures to be misread or missed entirely. If the board works
perfectly when stimulated externally over a long period of time, and if it
doesn't fail when perturbed, it's likely one or more of the switches is worn
out. That's when a different keypad becomes attractive. The KIM-1 Keypad was
never a thing of beauty or of any technical appeal. for purposes of preserving
the device, I'd say it's best to look for an exact replacement, in whatever form
it has to be obtained, and use an external keypad attached to the expansion
connector in order to retain use of the KIM-1.
Dick
----- Original Message -----
From: "Ethan Dicks" <ethan_dicks_at_yahoo.com>
To: <classiccmp_at_classiccmp.org>
Sent: Tuesday, April 10, 2001 2:21 PM
Subject: Re: Kim / Commie keypads
>
> --- Richard Erlacher <edick_at_idcomm.com> wrote:
> > It's pretty hard to tell whether it's the keypad or the circuit that's
> > malfunctioning. How did you determine it's the keypad itself?
>
> Looking at the schematic, it appears to be a simple matrix. Short a
particular
> X and Y line for the questionable key. If it "strikes", it's the keypad.
> If it still flakes out, it could be a component or trace.
>
> -ethan
>
>
> =====
> Even though my old e-mail address is no longer going to
> vanish, please note my new public address: erd_at_iname.com
>
> The original webpage address is still going away. The
> permanent home is: http://penguincentral.com/
>
> See http://ohio.voyager.net/ for details.
>
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>
Received on Tue Apr 10 2001 - 16:07:13 BST